Originally posted by rurockn Unfortunately I've been gone for a week and a half and this is one of my fav. topics. I'm also at work so this will be a short response.

I personally would prefer slightly higher compression with a reduced amount of boost to increase rev speed and retain a higher mid/low rpm torque while the upper end power/work will remain the same as the low comp. high boost engine. Correspondingly with the extremely efficient design of our chambers and accurate timing of dohc's it is more than reasonable to run 9.2 or 10:1 compression with an excess of 20psi and timing correction. I have stated in past posts that there are now hundreds of people running 4v modular fords with 10-20-30+psi that have very similar comb. chambers and 10.5:1 compression ratio while the 2v mod motors have bad detonation problems with this same setup. Now I'm not saying anyone should do this without extreme precautionary measures, just stating that it has been done many times over.

4v Heads by their nature are more detonation resistant. More quench area, as well as less combustion chamber surface area [in general].

Thanks for making it sticky Raf. Again, this is one of my favorite topics.

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Well, I havn't had time to read this entire post (I will later), so I'm not sure if anyone had mentioned this or not...

One reason why lower comression and higher boosted engines can make more power is because on the intake stroke, the manifold pressure is pushing on the piston, creating work. more psi = more work. look at a P-V (pressure vs. volume) diagram of two different boosted engines. you'll see that the intake stoke will create more + work with the higher boosted engine.

I think Andrew already mentioned about compressing air and it's affect on temps, right... with higher boost, the intercooler can cool more of the compressed air. and with less compression in the cylinder, it will not heat up as much in the cylinder as lower boost + higher compression...

OEM Turbo engines use low compression because they are afraid of some idiot running PEE water though it.
OEMs have to be almost bullet proof. So that is why you can pump up the boost some on most factory turbo cars without changing anything else like the turbo and IC.

I'm using this as an example...
In Japan, the late model MR2 turbo has 9:1 CR STOCK.
They where able to do this because they have decent fuel available.
The New Toyotas are great example of a detionation resistant 4V design. The 2ZZ-GE (cel. GTS) has 11:1 CR but will run on pee water without beating its self to death. I think the other secret is the VVT-i, running lots of overlap and lift seems to take the edge off of the CR. The 8 psi boost numbers are SCARY on the 2ZZ-GE

An 11:1 engine with boost and pump gas...who would have guessed?
CRs are starting to climb back up to where they were in the 60s...WHY? Can't be the gas (it still sucks)...I think you know why. I think the 2Ver has gone the way of the dinosaur, with the 3Ver looking like the 60s.

The future seems to be direct injection, high compression, and VNT turbochargers (sources from Honeywell/Garret say the BB turbo is yesterdays news, the VNT is tomorrom). Just think...no more discussions over the correct A/R ratio and the term lag will be long forgotten (thank god )

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ANOTHER FACTOR is you may be able to make an engine with High compression and a reasonable amount of boost aka 10psi or so, with some work and knowledge but you also have to realize how much stress that puts on the engine, ex head gasket, rings, etc. and longevity of the life of the engine

Thats why I had wiseco make me 2619 forged alloy pistons with compression of 8.7 to 1 with a 11mm dish. They are 20 over bore to give me a larger engine cc's. I figured so many people see these magazines of super imports and high boost but don't realize that almost all of us on this board (some exceptions) do not have the money nor the sponorship to support goals of high comp and boost to boot! Not to mention the fact that they don't mention in the articals that the engine gets rebuilt on a regular basis or that the car is a trailer queen and has only seen dyno's or less then 1000 miles in 2 years. Why do you think so many people have problems with aftermarket turbo's civics, probes, you name it. Realize that lower compression with 10psi is less taxing on your engine and will give it a much more reliable life. Since most of us don't have $$$ coming out of our butts, pick and reasonable boost level (mine will be 10psi street and 15psi track changed later after tuning) and lower compression. Don't think that you can make your car last long on high compression and high boost. Some trades must be givin to the boost gods if you plan to not have to rebuild often or spend lots of mulla to prevent rebuilds. to boost it's a bizz-atch

p.s. to help with low rpm increase in the begining of launch I plan on having a somewhat lightened flywheel and I'm debating on twin for smooth overall curve, not to mention top end rpm redline will be much higher do to the forged internals and millennia S rods and lower compresion so i'm hoping redline to jump to above 8200 rpms

Originally posted by geck0 ANOTHER FACTOR is you may be able to make an engine with High compression and a reasonable amount of boost aka 10psi or so, with some work and knowledge but you also have to realize how much stress that puts on the engine, ex head gasket, rings, etc. and longevity of the life of the engine

Thats why I had wiseco make me 2619 forged alloy pistons with compression of 8.7 to 1 with a 11mm dish. They are 20 over bore to give me a larger engine cc's. I figured so many people see these magazines of super imports and high boost but don't realize that almost all of us on this board (some exceptions) do not have the money nor the sponorship to support goals of high comp and boost to boot! Not to mention the fact that they don't mention in the articals that the engine gets rebuilt on a regular basis or that the car is a trailer queen and has only seen dyno's or less then 1000 miles in 2 years. Why do you think so many people have problems with aftermarket turbo's civics, probes, you name it. Realize that lower compression with 10psi is less taxing on your engine and will give it a much more reliable life. Since most of us don't have $$$ coming out of our butts, pick and reasonable boost level (mine will be 10psi street and 15psi track changed later after tuning) and lower compression. Don't think that you can make your car last long on high compression and high boost. Some trades must be givin to the boost gods if you plan to not have to rebuild often or spend lots of mulla to prevent rebuilds. to boost it's a bizz-atch

p.s. to help with low rpm increase in the begining of launch I plan on having a somewhat lightened flywheel and I'm debating on twin for smooth overall curve, not to mention top end rpm redline will be much higher do to the forged internals and millennia S rods and lower compresion so i'm hoping redline to jump to above 8200 rpms

when you get all your parts, get your rods shotpeened, (its like 7 bucks a rod) and get your assembly balanced !!! that way you can take it up to 8200 without worry

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when you get all your parts, get your rods shotpeened, (its like 7 bucks a rod) and get your assembly balanced !!! that way you can take it up to 8200 without worry

btw this is geck0 posting at ty's house
I understand this idea and since i work at a machine shop, it would be free-The problem with shotpeening the millennia rods is the fact that the wrist pin hole has a brass bushing that is sized to fit your wrist pin and if you shotpeen the rod you have to press out the bushing then replace it with a new one after you shotpeen, leaving the original one in during the peening to keep the mating surface on the rod the right size.

One Thing that everyoe here forgot to mention is timing.. I will cut and paste clip from another thread...

BTW To whomever mentioned that a supra on 6.9:1 compression and STOCK TURBOS MADE 900WHP you were fooled. The stock exhaust housing on the twins cant even flow enough air out without even on a 300 shot of N20 to make that much power. THe compressor sides of the stock twins cant flow enough air for 900hp even at 30psi each (if they can spin that high)

Here is the clip..

:quote:
Here is the deal with compression.. Low boost and high compression will make more power than low boost and low compression. High boost and High compression will not allways make more power than High Boost Low compression. The reason is many of things. You have to find a happy medium with a car. It depends on the flow of the head, intake manifold, exhaust manfiold, and the turbo at hand. Many of times with the lower compression you can run enough timing to more than make up the power, without detonation, and guess what your egt's go down. Many people do not know but retarded timing is just as bad for raising egt's as running lean is. 2* of timing on my car can drop egt's almost 75*C. This is where it comes to play.. When race gas (104 octane or higher) things stay the same except with more compression, timing, and boost. Methonal is a whole other ball game with stratospheric boost and compression levels.

I know of a low 11 sec street honda that runs 12.5:1 Compression and a T66 Turbo. Only about 5psi on the street but that is enough for high 12's. For race day he runs 20psi with C16 race gas. Has gone through is share of headgaskets though.. (bad tuning IMHO) Turbo spools great with that compression though.

I know of a low 11 sec street honda that runs 12.5:1 Compression and a T66 Turbo. Only about 5psi on the street but that is enough for high 12's. For race day he runs 20psi with C16 race gas. Has gone through is share of headgaskets though.. (bad tuning IMHO) Turbo spools great with that compression though.

Enjoy

I have a hard time believeing that a <2L motor can effetively spool a T6 and even if he does he is an idiot casue a T66 is way more compressor than he needs for 5 PSI!!!!! ALOT of turbo supras/RX7's run the T66 as a single turbo upgrade and never have i heard of one doing it w/o a 50 shot ot help spool... mind you a supra runs 3.0L over a hondas 2L...

Keep in mind Ric Stephens (aka purple minimonster 400hp miata) runs a T66 on his car. He doesnt get full boost tilll close to 6000 rpm.. Honda's dont get boost till about then also (as for drag cars) but it doesnt matter because they rev to over 8,000 and stay above there after each shift. Once Ric's new head is done he will be able to take the car to over 9000 and the T66 will be the best turbo for him. Trust me There are many of small displacment motors running big turbos. I know of a 2.0L DSM that is running a T72.. Its all on the flow of the motor, design of exhaust manifold and A/R ratios.

Keep in mind almost ALL of the Quick Class cars are running a T series turbo.

I never said it was a good street car. He was limited to 5psi because of the compression and pumpgas. At 5psi he is making ~270whp, and at 20psi he is making 490 whp. The car is a streetable drag car. Doesnt mean it is the best car for the street. The boy cant drive it on high boost and that is the only reason the car has not dipped into the 10's...

BTW it is a rare (AFIK) Hybrid T-Series with a T3 Turbine side. I have yet to see another car with that on it. IMHO it is not the right size turbo for the car. He could run a smaller turbo and make more power everywhere. I was just pointing an example of BIG turbo and Big compression.

I never said it was a good street car. He was limited to 5psi because of the compression and pumpgas. At 5psi he is making ~270whp, and at 20psi he is making 490 whp. The car is a streetable drag car. Doesnt mean it is the best car for the street.

IMHO it is not the right size turbo for the car. He could run a smaller turbo and make more power everywhere. I was just pointing an example of BIG turbo and Big compression.

Danny

That is exactly what i was thinkin.... saying it is "sterrable" sounds more like it... 5 PSI on a T66 aint much and i agree that a smaller compressor would make it a much more "drivebal" car thru the RPM's!

I am new to this probe thing, but I have been building cars since I was three(well, ok wrench fetching for my dad), and racing them since I was 15 or so. THIS IS JUST MY OPINION: You need to build your car right from the start. I'd get the heads machined for O-Rings, then build the bottom end, like a forged crank, connecting rods, and pistons. If you stay with 6-12 psi of boost you should be able to run 9.5:1 easily with premium fuel and a good tune up. Also boost does not always equal more power. If you have the same engine, same CR, same combustion chamber size, but engine A flows better than engine B, the the measured boost on engine A will be lower than that of engine B, but A will make more power than B, because it is more efficient.

Hmmm Forged Cranks and connecting rods are easy to find for any of the popular ford/Chevy V8...
But you must remember the KL engines aren't supported by any major tuners. So we are stuck with either $$$$ in custom parts or factory offerings.
I do agree about engine air flows being important,
but almost more important is turbocharger flow @ whatever PSI you plan to run. A Higher CR will make it more efficent, as will running more timing. But its a dangerous cocktail...use only with great caution.

Running a Giant turbo (T66 What happened to the 60-1 or 62-1 ) and lots of CR (12.5:1?? I doubt it runs very well, if at all on pumpgas)... Has some merit, but has its limits of how far you can take it (on gas). Now switching over to methonol will let you take it much further.

OT . JMO- Instead of slaping on big diesel turbos, I preffer to go with more technological advanced turbos like the Garret GT series.
One specific model (T04BB I think) flows 72lb per min (vs 68lb/min for the T66) and will end up with a lower boost threshold on any engine (vs. the old T66). Believe me there was been SERIOUS advancements in turbos since the design of the T66.

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Originally posted by white-probe as i recall, a high compression engine will fight againt the boost produced by a sc or turbo. If using one one these two you want a low compressioned engine.

nitrious is the only way you can go with a high compressioned engine. or have a high compressioned engine with no sc or turbo, use you basic bolt-ons.

SCC put 7PSI thru a Celica and it runs 11:1
You need ot read this whole post and some other info before you go stating that NOS is the ONLY way you can go wiht a high CR motor, cause that is a myth, and a common one at that

Once again this boils down to whoever's driving the car and/or the person putting money into the car. Higher static CR forces you to more finely tune the motor and limits the amount of total boost, but you get quicker spool and better off-boost throttle response. A lower static CR means you can boost higher, hence more fuel being burnt, and the tuning/ignition timing isn't as much of an issue, but you're not going to be seeing your potential in, say, city driving. Oh yeah, not to mention changing the intercooler size and piping, throttle body size, doing a P&P, etc. are some other variables that can be used to optimize the performance of your motor to personal needs, but you still won't make "the best" motor cuz the first motorhead that drives your car already knows what he'd change about it within the first 2 minutes of driving it.

Happy Tuning

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.. thinkin' the $200+ in Dynomat would better go on a nicer car sometime in the future. I still want a damn turbo and good tires though...

When Ford released the 2.3L carb turbo from 1979 to 1981 they ran 6 lbs of boost with a 9:1 CR.

When Ford rereleased the turbo motors in 1983 the turbo motors ran 14lbs boost with a 8:1CR

Ford reduced the compression ratio to facilitate more effecient cylinder filling. The 8:1CR can hold more air in the same volume because cooler air is denser. If you are running a normally aspirated engine then yes higher compression is desirable but on a turbo motor the lower compression will make more power due to the better cylinder filling.

I'm amazed at how many people you'll hear say, "Can't boost a ZE" I guess my philosophy behind everything is different. You either know cars or you don't. You know what will be a cause and effect. Not enough fuel = Boom. No Oil = Boom. Too much boost and not enough of either = Boom. Simple common sense thinking would help 90% of everyone not have any questions about the obvious. In any instance where raw materials are at stake, if you want more of something, you have to put more of the ingredients in. Air, Fuel, Spark = HP. I want more, ok.. Need more Air, Fuel and Spark. I want more HP again. Ok, Need more AIR, FUEL, SPARK. And guys, don't get smart about what I'm saying. I'm keeping this simple for the guys that don't understand. If you're baking a cake, and want it to supply more cake, you have to add more ingredients.

I want a 300whp Probe. So I bought 440cc Supra Fuel Injectors and a GReddy E-manage to control them. Plus a FPR, Vortech 12:1 FMU Walbro 255HP fuel pump. I wanted more HP, added more fuel.

Common sense will tell anyone that there are limits to everything. I know that my KLZE might beable to withstand 300whp. For how long? Who Cares! You have to expect set backs, blow engines, bad rings, blown head gaskets. It's called Racing! There are moving parts in the car. We have a luxury however. Back in the day, you would build and car and see what broke. Then pass that knowledge along. Well, its been passed along. So now we know that, "Hmm.. Ford built this car for a daily driver. Wonder if I can add 150+hp and still drive it daily and have it last 100,000+ miles?" And umm, the answer to that is "NO!" Not without re-engineering some things. Obviously no one builds and sells a new car with 200hp knowing that it can't take 201hp. Engineers take an enginer too its limits and back it way down. This is how you get cars that last 100,000+ miles. You make the engine and other components over powered for the weight to being with so they don't stress as much. Think about what we do to our cars! We basicaly screw up what millions of dollars in research and development went into. Do you think the work and engineering we do will be as successful in terms of making a car for every day driving? No! Again. This is my Racing Personality. Too many can't on the ProbeTalk forum. Here. I'll finish with my favorite saying. No need to talk anymore. I could type 500 page son this topic and never get through to some people and just waste my time and others so.. MY FAVORITE LINE TO SAY!

ANYTHING IS POSSIBLE WITH MONEY!!!

SPEND THE MONEY! BOOST YOUR CAR! ADD NITROUS!

It's all doable with money!

I will boost atleast 8psi to my ZE with a 35shot of nitrous. But I have some hellacious fuel mods and a GReddy E-Manage to Tune Everything. Will I blow this engine? Most likely if we don't get the tuning down right away. This is why alot of people stick with the same engine ratios and mods sometimes. They find they can get more hp/tq by tuning what they have and fixing the weak points then changing the whole setup around. I watched a $40,000 motor melt to pieces on a Dyno. It only had 1000 miles on it. What went wrong? Electrical problem caused detonation and fuel problems. BOOM! It happens. Just be ready for it. Expect the worse, and Live out the Best!

I think it's possible...
High compression engines are workable.
But since the higher compression generates MORE heat,
You need to do as much as possible to keep heat OUT of the intake charge.

BIG oversized intercooler with plenty of tube lenght to increase cooling effects (or an oversized air/water if you like dumping ice into it).
Efficent compressor, say 60-1 would be a great choice.
Efficent turbine wheel and turbine housing (IE not undersized),
A Stg 3 T3 turbine with an .81 A/R would be a good choice.

Now before the LAG police attack me, let me say that the high compression will help spool our efficent turbo.

Small turbos and small intercoolers are the reason why high compression engines explode (low octane too). People go out and purchase parts off factory turbo car that had low compression (with the ability to take a higher temp intake charge than a high compression engine) and expect 250-300WHP out of them. Psssss BOOM.
People defend these parts as well with comments like "DSM guys run 12s with them", but people don't relize that engine can flow big number and hold up to 400+HP...BONE STOCK. Not to mention people run 1800deg EGTs daily with NO problem. Not to mention handling higher intake temps than the KL03 or KLZE, not just because of compression but because it was designed to do so.

Also run the highest octane available (or that you can afford) and invest in a good knock sensing device as silent knock is the biggest killer of high compression turbo engines.

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i think GTRacer93 made the most sense out of anyone and their fancy formulas. you just do what you have to do. if you want more you have to give more of something. but it still doesn't help me choose the exact comp ratio to use. i wanted to go 8.5:1 but now reading all of this i think i want to go higher, but inbetween. maybe 9.2 and get benefits of both high and low comp. still not too high, and also low enough to take some good boost. the short lived FE3T, was 8.8:1. i'm sure they knew what they were doing, but i want some more comp for low rpms without boost for normal stop and go driving, and also high output at high rpms like 8K+. this will be a street car, with the potential to race. i'm over building, and not sparing much. just trying to make up my mind. after reading this most informative post, now i'm not sure at all what to use.
the good ol' F2T is only 7.8:1 and it does fairly well, and that's way lower numbers than anyone has mentioned in here and i see some ppl pushing a lot of boost through them, with the right mods ofcourse.
it seems to come down to everyone has their own preferences, and either engine tuned right will yeild great potential. but as far as lasting, is what i want to know. i want one that will last, yield great potential, and not the need to always having to tweak your settings to make sure you're at optimum so you don't blow something.

this is the 2nd best post i've read on a board, other one being gavin's all out suspension mods on mx6.com. this was way more informative though, but both just as interresting.

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Originally posted by ProbeGT90R i think GTRacer93 made the most sense out of anyone and their fancy formulas. you just do what you have to do. if you want more you have to give more of something. but it still doesn't help me choose the exact comp ratio to use. i wanted to go 8.5:1 but now reading all of this i think i want to go higher, but inbetween. maybe 9.2 and get benefits of both high and low comp. still not too high, and also low enough to take some good boost. the short lived FE3T, was 8.8:1. i'm sure they knew what they were doing, but i want some more comp for low rpms without boost for normal stop and go driving, and also high output at high rpms like 8K+. this will be a street car, with the potential to race. i'm over building, and not sparing much. just trying to make up my mind. after reading this most informative post, now i'm not sure at all what to use.
the good ol' F2T is only 7.8:1 and it does fairly well, and that's way lower numbers than anyone has mentioned in here and i see some ppl pushing a lot of boost through them, with the right mods ofcourse.
it seems to come down to everyone has their own preferences, and either engine tuned right will yeild great potential. but as far as lasting, is what i want to know. i want one that will last, yield great potential, and not the need to always having to tweak your settings to make sure you're at optimum so you don't blow something.

this is the 2nd best post i've read on a board, other one being gavin's all out suspension mods on mx6.com. this was way more informative though, but both just as interresting.

I think you will find that the answer lies within what you want. When you tell your engine shop what you want the car to do, they will say, less here and more there. I don't know if you're doing the work yourself but if you want a car that will last, consider that taking the highest compression route results in proper tuning of fuel mods. Lower compression is more forgiving. But if you have to boost all the time to get moving, then you will not lilke your car! Trust me. I know of a Turbo Supra that is fast fast fast and the guy hates the car. I beat him from light to light. Turbo lags too much. Once we hit open stretch though, I saw his tail lights from about 3 secs on till I couldn't see him anymore. If this your daily driver car I suggest you think about what Ford had the stock compression set to and up it a little from that. Then you'll know that a stock fuel system should be efficient enough if you stayed stock. But you're right, the only real way you have to go is to choose a middle level of compression 9.3:1 or something. KLZE 10:1, cams make it slow off the start. Compression makes it a beast there on though. I'm seen several boosted cars with 8.5:1 and the boost turned way up. If you can make the power with the engine and still be able to boost when you want it, why not take the extra power from the engine.

I just know that everyone makes things too complicated sometimes when someone just wants a simple answer as "Yes. if you want to maintain a daily driver and still beable to have the ability to boost a good amount, then go with a mid range compression".

So there you have it my friend. The answer usually lies within, you just want someone to back you up so you feel like you're right because you're unsure of yourself. You know the KL03 is a good motor and people have put 100k+miles on it with no problems other then leaking valve covers. You know the same block can go up to 10:1 and be run more then safe as it was in Japan. That tells you right there that you could go between those 2 compression and be just fine and probably better off then anyone running lower or higher compression then the 2 as tested by the car dealerships. Hope I aided you once more.

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